This invention relates to jacking mechanism for moving a string of well pipe essentially vertically along the axis of a well and relative to a drill rig.
The jacking mechanism of the present invention is of a general type disclosed in several prior copending patent applications and which is especially adapted in certain respects for lowering a lengthy and heavy string of casing into a well after drilling of the well. The jacking mechanism may be capable of handling a casing load of greater weight than could be suspended and lowered by the derrick, traveling block, lines, and drawworks of the rig, and thus may serve to effectively adapt a rig of relatively low capacity for handling heavy loads of casing during completion of the well. The jacking mechanism preferably includes a plurality of structures which extend downwardly beneath the rig floor generally parallel to one another and at different sides of the well axis, and which have portions serving as actuating units for moving one of two pipe supporting units upwardly and downwardly relative to the other to progressively lower an engaged string of pipe into the well. The two actuating units desirably take the form of piston and cylinder mechanisms extending generally vertically and connected to one of the pipe supporting units to move it upwardly and downwardly.
The present invention is especially concerned with a unique manner of positioning portions of a jacking mechanism of the above discussed type and other parts of a drill rig together beneath a rig floor, in a relation enabling reception of these various elements in a relatively confined space without adversely affecting the operation or accessibility of any of the parts. More specifically, the invention contemplates a unique relation between the jacking mechanism, a tubular mousehole member of the rig, and one or more ram type blowout preventers.
In accordance with the invention, the mentioned generally vertical subfloor structures of the jacking mechanism are positioned at locations offset circularly about the well axis from the mousehole, with the blowout preventer or preventers being located at approximately the well axis and projecting laterally outwardly at a location circularly between one of the subfloor structures of the jacking mechanism and the mousehole. In some arrangements, the blowout preventer may project outwardly at a location circularly between the mousehole and a power cylinder of one of the actuating units of the jacking mechanism. In other instances, one or more of the ram type blowout preventers may project outwardly at a level below the lower end of such a cylinder, and circularly between the mousehole and a support or base which takes load forces from the cylinder.